ESMO 2020: highlights in breast cancer.

Despite the ongoing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, results of several pertinent studies in the field of breast cancer (BC) were presented in a virtual format at the 2020 European Society of Medical Oncology (ESMO) Congress. Early results of the MonarchE trial investigating the addition of the cyclin-dependent kinase (CDK) 4/6 inhibitor abemaciclib to standard adjuvant endocrine therapy indicated a lower recurrence rate in the combination group in a high-risk population of patients with early stage hormone receptor (HR)-positive/HER2-negative BC. In contrast, the PALLAS study evaluating adjuvant palbociclib could not confirm these results. Subtle differences in the respective trial populations, a higher discontinuation rate in PALLAS, or substance-specific differences may be responsible. In HER2-positive early stage BC, long-term results of the ADAPT-TP trial support the notion that chemotherapy-free treatment may be possible in a subset of patients with favourable response to HER2-directed therapy without compromising long-term outcome. The phase III IMpassion031 trial evaluated the addition of atezolizumab to neoadjuvant anthracycline/taxane-containing chemotherapy in triple-negative BC (TNBC). A significant improvement in terms of pathologic complete remission rate was observed but data concerning long-term outcome must be awaited. Final overall survival (OS) analysis of IMpassion130 confirmed the clinically relevant OS improvement observed with the addition of atezolizumab to first-line nab-paclitaxel in metastatic PD-L1 positive TNBC. In contrast, no benefit was observed with the addition of atezolizumab to solvent-based paclitaxel in a similar population. This contradiction is commonly explained by the need for corticosteroid co-medication with conventional paclitaxel, but the exact reason remains poorly understood. Antibody-drug conjugates (ADCs) have been successfully established in HER2-positive breast cancer; in TNBC, the phase III ASCENT trial compared the ADC sacituzumab govitecan with chemotherapy by physician's choice in pretreated metastatic patients. A significant improvement in terms of progression-free survival and OS was observed rendering this drug a potential novel standard in this patient population.